Government health guidelines in France on what constitutes a good breakfast are: a milk product, a fruit, a source of carbohydrate and a drink. So a croissant, yoghurt and fruit juice, or a chocolate drink, "tartine" of bread-and-butter and a stewed-fruit compote, both typical French breakfasts, are ideal.
Lunch is early and traditionally long, Lunch and dinner are both full meals, comprising two and possibly three courses. No family meal is set on the table without a salad (complete with dressing, since there is no suggestion, ever, that the pleasure of eating should be curbed by anything but appetite) either as a first course or as a course on its own between starter and main course.
Snacking is viewed as rather lax, although a snack may be taken about 5pm - again, yoghurt, fruit, coffee - to stave off the hunger pangs, since dinner can be as late as 9pm.